This invention relates to a device for the administration of powdered medicaments by inhalation, more particularly to a multiple-dose inhalation device with metering means for dispensing pre-determined doses from a medicament reservoir.
European Patent 407028 discloses a multiple-dose inhalation device in which a dose of medicament is metered by abrading a fixed volume from a compacted body of powdered medicament. In a preferred embodiment of this device the compacted body of medicament comprises a cylinder which is held within a reservoir and which fits over an inner mandrel. The mandrel provides support for some or all of the medicament compact and provides an axis around which the reservoir and compact is turned in order to abrade a dose of medicament from the compact. The metered dose is then entrained in a through-going pathway of the device and is inhaled by the patient, the means for abrading being, for example, a helical blade.
The device of EP 407028 was improved in EP 691865 by providing a shuttering system to isolate the compacted body of medicament from the through-going pathway of the device. However, during transport powder still tended to leak from the medicament compact to the outer mechanism.
We have now found that this leakage can be greatly reduced by provision of a partial sealing means between the medicament reservoir and the inner mandrel of the inhalation device. Surprisingly it has been found that although a gap must be left in the sealing means in order to accommodate the pathway between the medicament reservoir and the dispersion chamber leakage is substantially reduced. Another advantage of the seal is that it provides a frictional brake which allows the ratchet mechanism rotating the medicament reservoir to cause abrasion of the medicament compact therein to return to its starting position without concomitant movement of the medicament reservoir.
Thus, according to one aspect of the invention, there is provided a medicament inhalation device including a housing having a through-going pathway connecting an air inlet with an air outlet, a medicament reservoir adapted to receive a compacted body of powdered medicament, an inner mandrel around which the medicament reservoir rotates and metering means for dispensing a predetermined dose of medicament from the reservoir into the pathway, the metering means including means for abrading the compacted body; characterised in that there is provided between the medicament reservoir and the inner mandrel of the device a sealing means extending round less than 360xc2x0 of the mandrel.
In a further aspect of the invention the sealing means is adapted to provide a frictional braking force on the medicament reservoir sufficient to prevent movement of the medicament reservoir when the ratchet mechanism designed to cause rotation of the reservoir is returning to its starting position but which force is not so large as to make the device difficult to operate by a child or infirm adult. Typically this force will comprise a torque of between 0.1 and 0.6 Newton meters (Nm), preferably between 0.2 and 0.5 Nm and most preferably about 0.4 Nm.
The sealing means may be produced as an integral feature of the inner mandrel in a single production operation. This may be particularly advantageous when the material of construction of the mandrel is such that the sealing means feature is suitably resilient to produce the required seal and/or frictional braking effects.
The sealing means may be added to the mandrel during production by any standard process method, allowing the mandrel body and sealing ring to be formed from different materials. One such method is known as insert moulding. In insert moulding the mandrel body is formed by a standard moulding process. The mandrel body is transferred to a separate tool where the sealing means is moulded into position on the mandrel body. This process gives a good mechanical fit between the mandrel body and the sealing means but no adhesive or chemical bond. A second method is co-moulding. The mandrel body is formed by a standard moulding process. Co-incident with or slightly after the formation of the mandrel the sealing means is moulded in place using the same machine. In this process a chemical or adhesive bond is formed between the sealing means and the mandrel body.
Alternatively the sealing means may comprise a separate partial sealing ring. It is preferred that the sealing ring be formed in a single moulding process rather than being provided as a complete ring and cut to size.
The sealing means may conveniently be produced from any suitable resilient material. It is important that the material be compatible with the medicament and excipients used to form the medicament compact. ABS or Polyolefin plastic materials are preferred and a particularly preferred material is polypropylene.
The ring may be of any cross sectional shape capable of providing a good seal. A particularly advantageous shape for the cross section is a generally xe2x80x98Vxe2x80x99 shape with the point of the xe2x80x98Vxe2x80x99 aligned to face the medicament compact. Preferably the arm of the xe2x80x98Vxe2x80x99 next to the inner mandrel is flush with the mandrel. The section of the ring in contact with the inner mandrel may be thicker and, therefore, less flexible than the section sealing the medicament reservoir. Where the sealing means is formed integral with the mandrel the V may be formed by a flap extending from the mandrel.
The proportion of the circumference of the mandrel sealed by the sealing means should be as high as possible, with the gap in the sealing means being sized to accommodate the pathway between the medicament reservoir and the inhalation chamber. Preferably the sealing ring should extend for about 250xc2x0-330xc2x0 around the mandrel and more preferably for about 300xc2x0.
Since the sealing ring is formed from resilient material it can be held in position during assembly of the device by this resilience. During use axial and rotational movement may be constrained by shoulder features on the mandrel collar. Additionally, or alternatively, the sealing ring may be held in position by an adhesive bond between the sealing ring and the mandrel.
Thus, according to a further aspect of the invention there is provided a sealing means comprising a partial ring extending about 250xc2x0-330xc2x0, preferably about 300xc2x0, of a full ring circumference, whose cross section is generally V shaped.